I am talking about running a 50-100' snake in addition to the 15-25'
lengths on stage. I have used Canare or Mogami quad cable since 1986, but
have never taken the time to A/B it to three conductor cable. A snake made
from 3 conductor cable would definitly be less expensive as well as easier
to obtain as long as RFI will not be a concern. Who knows if it will or not
until after the purchase is made and we are off and running. I don't really
think there will be any problems in this venue, so if everyone thinks that
the sound quality would be improved by not using quad cable then I would be
inclined to build some additional cables from Mogami three conductor to use
on stage instead of my normal quad cables.

I will be using Schoeps and Neumann condensers, Beyer and Royer ribbons, and
a few dynamics as well as Radial active DIs. I will also be using two Cooper
Sound mixers linked together which have Jensen transformers and very quiet
high gain mic pres.

Now would all this make an audible difference or am I just spending money
and time?

Brad Harper


"Justin Ulysses Morse" wrote in message
...
Brad Harper wrote:

I was inquiring about having a 12 channel snake built for an upcoming
live
jazz show shot on HDTV. I requested that it be built with Canare or
Mogami
quad cable to a length of 100 feet. The person told me that they only
used
Mogami three conductor cable for long snakes because the quad cable
doesn't
sound as good due to the capacitance of quad cable over 100 feet.

I have used 600 feet of Canare DT12 cable before, but of course I have
never
had the opportunity to A/B the signal to standard mic cable. The issues
of
RF resistance have always been the main concern.

What opinions do you guys have on this.


I actually don't have an opinion, but I do have the facts required to
form one. You can calculate the exact effect of the cable capacitance
yourself. Here's what you do: Look up the cable capacitance in the
manufacturer's spec sheet. The lowest spec I know of is Belden 1800F
which is about 13pF per foot. The highest of any reputable brand for
mic cable is probably going to be about 60pF per foot for star-quad.
Multiply this by the length of the cable and you'll have a s figure for
the "shunt capacitance" hanging across each microphone output as a
result of the cable. This may not be the only shunt capacitance, since
many mike preamps evade good anti-RFI practices by hanging a capacitor
from each input lead to chassis ground. But I digress. Suppose you
have 100 feet of cable with 60pF/ft capacitance. That's 6000pF total,
or .006µF, or 0.000000006 FARADS of capacity. This capacitance will
interact with the impedance of the circuit it's in (the source
impedance of the microphone in series with the cable's resistance and
in parallel with the preamp's input impedance). This will generally be
approximately equal to the microphone's output impedance alone, so you
can just use that. The nominal value for most microphones is 150 ohms,
but a modern transformerless condenser microphone will be much lower
and an old transformer-coupled ribbon mike will be a lot higher.
Now you can use these numbers to calculate the frequency at which you
have a -3dB roll-off (it gets worse than that as you go up in
frequency). The formula is:

f=1/(2¼ZC)
[frequency equals the reciprocal of the product of two times pi times
impedance times capacitance]

Using 150 ohms and 6000pF capacitance, we get a -3dB point of 176.8kHz.
Doesn't seem like a problem to me. But imagine if you double the
source impedance, doubled the cable length, and doubled the cable
capacitance. You'd be down to 22kHz like that. And though you may NOT
double all those things, you should realize that running multiple
low-pass filters (which is what this is) in series will have the exact
same effect. So although a single 176kHz LP-filter may not be audible,
a bunch of them at various places in your signal path will be. So it's
something to keep in mind. Exactly where this becomes worth
sacrificing time, money, or other performance parameters is something I
don't have a fully developed opinion on.

ulysses